In recent years, there has been an increasing demand for interior lighting devices, especially for commercial lighting devices, to be smaller and brighter. As a light source to meet the demand, metal halide lamps (HID lamps) have been attracting attention.
To meet the demand of smaller lighting devices for interior use, a first conventional metal halide lamp includes, as shown in FIG. 11, an outer tube 111 that is made of hard glass, an arc tube 130 that is provided inside the outer tube 111, and a sleeve 120 that is made of fused quartz, arranged between the outer tube 111 and the arc tube 130, and surrounds the arc tube 130 (see Patent Document 1).
Furthermore, to make the lighting devices even smaller, a second conventional metal halide lamp includes, as shown in FIG. 12, a fused quartz tube 311 that has a closed part at one end, and a pinch seal part 321 at the other end, and an arc tube 330 arranged inside the fused quartz tube 311 (see Patent Document 2).    Patent Document 1: Japanese Laid-Open Patent Application No. 10-283996; and    Patent Document 2: Japanese Laid-Open Patent Application No. 11-96973.